This invention relates to devices for maintaining a substantial seal to an isolated environment while allowing the introduction and withdrawal of a probe member. The invention relates particularly to a probe inlet device and method for facilitating the introduction of a sample onto a chromatography column.
A number of procedures, particularly chemical testing procedures, require the introduction of a probe member into an isolated environment for injecting or extracting a sample of the material. For example, chromatography involves introducing a sample of material onto a column through which a liquid or gas eluent or mobile phase is passed. The column is composed of a second or stationary phase which may be a solid or liquid onto or into which the sample may be absorbed or dissolved.
In gas chromatography, where the mobile phase is a gas and the stationary phase is either a liquid or solid, the sample was commonly introduced through a septum with a suitable syringe. The syringe needle was adapted to penetrate completely through the septum so that the sample could be injected into a sample introduction area at one end of the column. The septum material formed a seal around the syringe needle while the needle was inserted and then closed up the puncture hole and formed a seal once the syringe needle was withdrawn.
There were several problems associated with the use of septums in introducing a probe into an isolated environment. One such problem was that the septum material was damaged after repeated injections leading to leaks through the material which allowed material to escape from the isolated environment. Such leakage resulted in altered readings in the case of chromatographic devices. The leaks also allowed oxygen from the atmosphere to enter the isolated environment. In chromatography such oxygen leakage damaged the stationary phase and altered its performance. The septum material also commonly contained elastomeric polymers which degraded when exposed to elevated temperatures. Such degradation released foreign material from the septum into the isolated environment. In chromatography, this release of vaporized material from the septum was referred to as septum bleed and was undesirable in that the released material often damaged the column material or altered the response of the instrument detectors. Septum bleed was also accompanied by loss of elasticity in the septum material which resulted in decreased ability of the septum material to seal the hole caused by the needle insertion, and reduced the lifetime of the septum.
U.S. Pat. No. 4,854,181 and German Patent No. 34 00 458 both to Gerstel show septumless sample injection and extraction devices specifically adapted for use in gas chromatography. Both devices include a valve body having an annular outer seal and an inner seal that includes a sealing member adapted to be thrust obliquely out of a sealing position by contact with an injection or extraction probe as the probe is inserted through the valve body. The seal member is a ball adapted to seat in a sealing ring in the German patent and an elongated sealing member adapted to seal against an O-ring in the U.S. patent. In both devices, a spring mechanism is used to hold the sealing member in the sealing position when the probe is not inserted through the housing and to return the sealing member to the sealing position as the probe is withdrawn.
Although the Gerstel devices avoid some of the leakage problems associated with septum-type sample injection and extraction arrangements, there were still several problems associated with such septumless devices. Both Gerstel devices required elastomeric O-ring seal members in the inner seal arrangement. These O-rings were made of materials that broke down at high temperatures so a to lose their elasticity and ability to seal. The O-ring material breakdown also released foreign material into the chromatography column. Furthermore, both Gerstel devices required the probe member to contact the particular seal member at an angle and provide a substantial lateral force to unseat the seal member. Such lateral force damaged the relatively fragile probe members, particularly probe members used in automated samplers which inject the probe member rapidly.
It is therefore an object of the invention to provide a probe inlet apparatus for facilitating the introduction and withdrawal of an elongated probe member that overcomes the abovedescribed problems and others associated with probe inlet devices. It is also an object of the invention to provide a method for introducing a probe into an isolated environment while maintaining a substantial seal to the isolated environment.